Undesirable nuisance plant growth such as algae, bacteria, mold and fungus, have been a common problem for surfaces in both fresh water and seawater areas. For example, swimming pools, fountains and other manmade vessels that hold water are subject to fouling by algae.
Past methods for preventing algae type plants have had numerous problems. Current surfacing agents for treating algae growth are basically toxins that also can be toxic to humans above threshold concentrations. For example, tributyl tin has been shown to be an effective toxin and has been incorporated into marine based paints for the hulls of boats. While gradual release of the toxin when the boat is underway is considered acceptable, a boat in port can generate unacceptable concentrations of toxin.
Certain preparations of Titanium Dioxide can be bright white in color, and are often used in commercial paint formulations. See U.S. Pat. No. 5,142,058. However, these preparations are made deliberately so as to be photo-inactive where any form of photo-activity is regarded as a negative characteristic, because the organic binder containing the pigment can be ultimately attacked and destroyed.
A standard toxin agent includes chlorine. Chlorine is a standard means for disinfecting swimming pool water and drinking water. However, disinfectants such as chlorine become spent and must be replaced over time with repetitive additional costs. Heavy chlorination of microorganism-containing water can also result in suspected carcinogenic by-products such as trihalomethanes.
Toxin release agents are not only inferior due to their health effects on higher order plants and animals, but also because they represent a consumable item that must be eventually replaced.
Many types of algicides function as light blockers, absorbing the light necessary for algae growth. This involves dissolving one or more dyes in the water whose net absorption spectrum matches that of the algae. Thus, the water is dyed with an unnatural shade of blue or green that can be aesthetically unappealing. These algacides are also subject to eventual decomposition and require periodic replenishment.
Photocatalysts have been used for the decomposition of organics. See U.S. Pat. Nos. 4,863,608 to Kawai; 5,244,811 to Matthews; 5,332,508 to Foster; 5,501,801 to Zhang; 5,541,096 to Nomura; 5,547,823 to Murasawa; 5,593,737 to Meinzer et al.; and 5,616,532 to Heller et al. However, these patents are limited to requiring specific oxide values of TiO.sub.2 and WO.sub.3. None of these patents varies the oxides themselves.